The present invention relates to cooling arrangements for protecting the walls of metallurgical furnaces from heat, and more particularly to shaft-furnace coolers.
The invention can be advantageously applied for the protection of blast-furnace shells.
Because of elevated temperatures created in the working space of a blast furnace, the shell thereof is subjected to severe heat. Therefore, special arrangements are called for to insure mechanical strength of such shells and to protect them from heat loads. The arrangements in question are plate coolers which are usually mounted on the furnace shell at the side of the furnace working space.
It is modern practice to intensify the blast-furnace process by raising the blast temperature, increasing the amount of oxygen contained in the blast, or else by building up pressure in the furnace space. The above factors are detrimental to the operation of heat-protecting arrangements, placing more stringent requirements upon their ability to resist heat.
There are known in the art plate coolers which comprise a cast-iron plate with built-in steel pipes whose open ends extend beyond the plate and through the furnace shell. The pipes are connected through said ends with the furnace cooling circuit through which circulates a coolant, such as industrial or chemically treated water, or vapor-water mixture.
In the course of the blast-furnace operation, the plate is exposed to heat loads which vary timewise. As a result, the plate tends to change its geometrical dimensions, expanding and contracting. The plate expansion and shrinkage adversely affect the pipes which are rigidly connected therewith. The process of manufacturing coolers is such that it causes embrittlement of steel pipes which are subjected to carbonization in the process of casting molten iron therein. The ends of the pipes extending through the furnace shell are usually welded thereto. With the iron plate acting upon said pipes, there are created in the pipes periodically variable pressures which bring about their destruction. As a result, the coolant passing from the furnace cooling circuit penetrates through the damaged pipe into the furnace working space. This calls for higher fuel input per unit of production because of the heat losses required for the evaporation of the escaped coolant. In some cases, the penetration of considerable amount of coolant to the furnace may even disrupt the furnace operating process.
At present, due to the lack of reliable and prompt trouble-shooting techniques, it takes considerable time and human effort to spot and disconnect the damaged pipe. The attending personnel involved in such operation are compelled to work under conditions of severe gas contamination and high temperatures.
It is deemed necessary to point out still another disadvantage of the hereinbefore described coolers. There is provided in the furnace cooling circuit a plurality of coolers which are connected thereto, and with gravity circulation of the coolant. This type of coolant circulation depends for its rate on the average heat load acting on the coolers. With the lining being broken away from the surface of the cooler plate, the latter is exposed to severe heating which can be eliminated only by increasing the rate of vapor-water mixture circulation through the pipes intended for cooling the plate. As mentioned above, however, the rate of circulation depends solely on the average heat load acting on the group of coolers, which practically remains constant. Therefore, the increased amount of heat effecting a separate plate results in greater amount of vapor in the pipes cooling this plate, which, in turn, causes its overheating and fusion.
For the purpose of improving the cooling of the cooler plate during a sudden increase of the flow rate of heat effecting said cooler and to eliminate the possibility of water penetration into a metallurgical furnace, there has been developed a cooler comprising a plate with pipes whose ends at one side thereof are built into said plate. The pipes are filled with a coolant and sealed. The other ends of the pipes, which are mounted higher than those filled with water, extend beyond the plate and pass through the furnace shell into a cooling chamber where they are fixed. Circulating in the cooling chamber is a coolant. The cooling chamber is arranged exteriorly of the furnace and connected to the cooling circuit thereof.
The improved cooling of the plate of each separate cooler has been accomplished by way of sealing the ends of the cooler plate pipes, whereby each pipe is provided with its own circuit wherein the vapor-water mixture circulation is determined by the heat loads acting on such circuit. The rate of vapor-water mixture circulation in the plate-cooling pipes increases with the heat load acting on the plate, thereby providing for reliable cooling of said plate.
The use of such cooler practically eliminates coolant penetration into the furnace in case of damage to the sealed pipe, since there is but a negligible amount of coolant contained therein, water with the furnace cooling circuit, wherein circulates and is separated from the interior of the damaged pipe by the wall of the latter. This being the cooler construction, the pipe is surrounded with the cast-iron plate, having therefore, its entire surface exposed to heat. It happens that certain heat flows cause abundant formation of vapor in the part of the pipe which is fixed in the plate, and the condensate, formed in the free part of the pipe due to condensation of vapor passing thereinto through a cooling chamber, is prevented from descending to the lower part of the pipe. Thus, the water from the part of the pipe fixed in the plate is rushed to the upper part of the pipe. This results in the overheating of the pipe and plate walls because of the absence of the heat outlet leading to the furnace cooling circuit, and the destruction of the cooler thus becomes inevitable.
To eliminate the above-mentioned disadvantage, there has been proposed a cooler for a metallurgical shaft furnace, comprising a plate with built-in pipes whose ends at one side thereof are filled with a coolant and sealed. The other ends of said pipes are disposed above those filled with the coolant and extend beyond the plate and through the furnace shell into a cooling chamber to be fixed therein, said chamber being connected to the furnace cooling circuit with a coolant circulating therethrough. Fitted into each said pipe is a pipe-insert with a diameter substantially less than that of the main pipe, so that open ends of the inserted pipe have no contact with closed ends of the pipes, the generatrix of the inserted pipe coming in contact with that of the pipe facing the furnace shell.
The heat removed from the plate is used to heat up the water in the sealed pipe. The resultant vapor-water mixture rises to the coolant-free end of the pipe wherein the vapor is condensed on the pipe wall, cooled with the coolant flowing through the cooling chamber and circulates within the furnace cooling circuit, and then drains down through the inserted pipe. In such a manner the coolant flow is separated into two flows, namely: the vapor-water mixture flow rising to the water-free end of the pipe, and the condensate flow passing down to the portion of the pipe in contact with the plate. The cooler was thus enabled to function faultlessly in the conditions of severe heat flowing out of the furnace working space; this being the advantage over the previously described cooler.
However, the hereinabove described cooler is complicated in construction due to the difficulty of fitting smaller-diameter pipes into the plate-cooling pipes, the former requiring complex configuration which resembles that of the latter.
It is therefore an object of the present invention to improve operating reliability of a shaft-furnace cooler by means of providing reliable cooling of the cooler plate exposed to heat evolved in metallurgical furnaces.
Another object of the invention is to increase the furnace campaign by means of enhancing operating durability of coolers due to improving the heat resistance of their plates.
Still another object of the invention is to reduce the cooler weight.